Box-shaped plastic housing of integrally molded resin

ABSTRACT

A box-shaped plastic housing of integrally molded resin comprises a flat-shaped bottom wall having a peripheral edge and an upright wall extending upwardly from the peripheral edge of the bottom wall. The bottom wall and the upright wall cooperatively define an integral box-shaped molded product. The thickness of the bottom wall is in the range of two-thirds to one-third with respect to the thickness of the upright wall. The bottom wall is provided with at least one rib on its inner surface. The housing is produced by an injection molding process using a mold having a mold cavity which is provided with a groove on the inner surface of the cavity corresponding to each rib.

This application is a division of application Ser. No. 07/775,561, filedOct. 15, 1991, now U.S. Pat. No. 5,254,304.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a plastic housing structure, a process forproducing the same, and a mold structure used in this process. Such aplastic housing structure is used for home electric or electronic units,toys, telephones, office automation machines, and the like, and moreparticularly is suitable for portable personal computers portablewordprocessors, or the like.

At present, portable units, in particular, notebook type personalcomputers, or portable wordprocessors have been made lighter and lighterin weight. It should be noted that the material of the housing structureof these machines has been changed from a heavy metal to a plasticmaterial which is lighter in weight and of a reduced specific gravity.However, in these products, the weight of housing is still about onethird of the total weight of the product. Thus, it has been required toreduce the wight of the housing structure.

2. Description of the Related Art

A conventionally known plastic housing for notebook type personalcomputers or portable wordprocessors has been required to be strong andeasy to form. In this respect, it has been desired that the thickness ofthe housing be as uniform as possible, i.e., the thickness being 3 to 5mm, or about 2.5 mm at a minimum. The specific gravity of a plasticmaterial is generally 0.95 to 2.0, and the specific gravity of a plasticmaterial of high strength is about 1.1 to 1.7. Therefore, it would seemimpossible to reduce the weight i.e., the specific gravity, of theproducts by reducing the weight of housing material. One approach tothis problem is to reduce the thickness of the housing walls. However,with this solution there arises the following problems in the prior arttechnique for forming plastic housings.

Thus, the following problems would arise if the thickness of the housingwall was reduced to 1.0 to 0.7 mm.

1) In general, the deformation of a plate due to a bending stress variesby amount inversely proportional to the thickness squared of the plate.Therefore, if the thickness of a plate is reduced by one-half (1/2), thedeformation thereof will be increased four times. In such a manner, ifthe thickness of a plate is reduced, it becomes too easily deformableand, thus, the housing would become too weak to protect the contentsthereof.

2) If the thickness of the housing wall is reduced, when the housing ismade by injection molding, the melted resin must flow into a cavitywhich has the thin, wide area. Thus, a resistance to flow becomes veryhigh and the pressure necessary for flowing the melted resin becomesalso high. Therefore, an injection molding machine having a largeinjection capacity must be used. Also, if the pressure is to be thusincreased, a large force is exerted on the mold to open the same, sothat a variation of thickness of the housing wall might occur and finsmight be generated. In addition, if the thickness of a housing wall isthin, the heated, molten resin comes into contact widely with the innerwall of the mold cavity, when flowing therein, so that the resin israpidly cooled and thus the temperature of the resin is lowered. Thismeans that the viscosity of the resin is increased and thus a part ofresin might become solid before having reached to the terminal portionsof the mold product which causes a so-called "short shot".

3) In order to prevent the above-mentioned variations and "short shot",if the thickness of the housing wall is increased at peripheral portionsthereof and if the product is provided with ribs which serve as passagesfor the melted resin when forming the same by molding, the followingsecondary problems will arise. Namely, the resin will first flow intothe portions of low resistance, i.e., the peripheral portions and theribs, so that gas which could not be discharged to the outside,accummulates at a bottom wall and thin wall portions of the housing and,therefore, a so-called "burned mark (spot)" will arise due to "shortshot" or a compression of gas.

4) In a final discharge process for taking the product out of the metalmold, if the product has a thin wall portion and if the product ispushed by a pusher engaging the thin wall portion thereof in the samemanner as a general product, the thin wall portion may be damaged ordeformed by the pusher, since such a portion has not been sufficientlysolidified yet.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a light weight plastichousing structure, a process for producing the same, and a moldstructure used in the same process, capable of overcoming theabove-mentioned problems in the prior art.

According to the present invention, there is provided a box-shapedplastic housing of integrally molded resin, said housing comprising asubstantially flat-shaped bottom wall having a peripheral edge, anupright wall extending upwardly from said peripheral edge of said bottomwall, said bottom wall and said upright wall cooperatively defining anintegral box-shaped mold structure, and the thickness of said bottomwall being in the range of from two-thirds to one-third with respect tothe thickness of said upright wall.

In one embodiment, the average thickness of said upright wall ispreferably not more than 3.0 mm.

In another embodiment, it is advantageous that said bottom wall and saidupright wall have respective surface areas, and the surface area of saidupright wall is not more than one-half of the area of said bottom wall.

In still another embodiment, it is advantageous that said bottom walland said upright wall have respective inner surfaces, said respectiveinner surfaces cooperatively define an inside surface of said box-shapedstructure, and said bottom wall is provided with at least one ribstructure on said inner surface thereof.

In further embodiment, it is also advantageous that said rib structureis provided with at least one cylindrical boss having an axisperpendicular to a direction along which said rib structure extends,said cylindrical boss being used as a connector, e.g., as a threadedhole for a screw or a non-threaded hole for a self tapping screw andalso used for extruding said molded product.

Otherwise, it is advantageous that at least two of said rib structurescross mutually at an intersection, said rib structures being provided atsaid intersection with a cylindrical boss having an axis perpendicularto the directions along which said rib structures extend, and saidcylindrical boss being used as a connector, e.g., as a threaded hole fora screw or a non-threaded hole for a self tapping screw and also usedfor extruding said molded product.

According to another aspect of the present invention, there is providedwith a process for producing a box-shaped plastic housing integrallymolded with a resin; said housing comprising a substantially flat-shapedbottom wall having a peripheral edge, an upright wall extending upwardlyfrom said peripheral edge of said bottom wall, said bottom wall and saidupright wall cooperatively defining an integral box-shaped moldstructure, the thickness of said bottom wall being in the range of fromtwo-thirds to one-third with respect to the thickness of said uprightwall, said bottom wall and said upright wall having respective innersurfaces, said respective inner surfaces cooperatively defining aninside surface of said box-shaped structure, and said bottom wall beingprovided with at least one rib structure on said inner surface thereof;and said process comprising an injection molding process using a moldhaving a mold cavity, said mold being provided with at least one grooveon an inner surface of said cavity corresponding to said rib structures.

In one embodiment, said rib structure is provided with at least onecylindrical boss having an axis perpendicular to a direction along whichsaid rib structure extends; said process comprising a step fordischarging said plastic housing from said cavity by pushing saidcylindrical boss with a cylindrical sleeve knockout pin.

In still another aspect of the present invention, there is provided amold structure used for producing a box-shaped plastic housing ofintegrally molded resin, said housing comprising a substantiallyflat-shaped bottom wall having a peripheral edge, an upright wallextending upwardly from said peripheral edge of said bottom wall, saidbottom wall and said upright wall cooperatively defining an integralbox-shaped mold structure, the thickness of said bottom wall being inthe range of two-thirds to one-third with respect to the thickness ofsaid upright wall, said bottom wall and said upright wall havingrespective inner surfaces, and said respective inner surfacescooperatively defining an inside surface of said box-shaped structure;said mold structure comprising at least two injection molds definingtherebetween a mold cavity, one of said injection molds, which definessaid inside surface of said box-shaped structure, being provided with atleast two injection gates for injecting the resin into said cavity.

In one embodiment, said one of injection molds, which defines saidinside surface of said box-shaped structure, is provided with at leastone telescopic or knockout pin for removing any gas finally remaining insaid cavity due to resin injection by said injection gates.

In another embodiment, one of said injection molds, which defines saidinside surface of said box-shaped structure, is provided with at leastone groove corresponding to said rib structures of said housing, and atleast two injection gates on said grooves for injecting the resin intosaid cavity, and there is also provided on said grooves at least onetelescopic or knockout pin of a material such as a sintered alloy orhaving an associated structure for selectively removing any gas finallyremaining in said cavity due to resin injection by said injection gates.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a schematic perspective view of a model I or II, FIG. 1(b)is a cross-sectional view taken along line b--b in FIG. 1(a) and showingthe model I, and FIG. 1(c) is the same cross-sectional view as FIG.1(b), but showing the model II;

FIG. 2(a) is a plan view of a housing according to an embodiment of thisinvention, and FIG. 2(b) is a cross-sectional view taken along line b--bin FIG. 2(a);

FIG. 3(a) is a perspective view of a model shown in FIG. 2, thethickness of the upright wall being 1.0 mm, and FIG. 3(b) is aperspective view of the same model as in FIG. 3(a), but with thethickness of the upright wall being 2.0 mm;

FIG. 4 shows results of a simulation of resin flow for determining amold structure;

FIG. 5 is a cross-sectional view showing an embodiment of a moldstructure according to the present invention;

FIGS. 6(a), 6(b), 6(c) and 6(d) show embodiments of a boss or knockoutpin structure; and

FIG. 7 is a plan view of a housing (i.e., a lower cover) of thisinvention used in a notebook type personal computer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, wherein FIG. 1(a) is a schematicperspective view of model I or II, FIG. 1(b) is a cross-sectional viewtaken along line b--b in FIG. 1(a) and showing the model I, and FIG.1(c) is the same cross-sectional view as in FIG. 2(b), but showing themodel II;

The box-shaped plastic housing structure 1 comprises a substantiallyflat-shaped bottom wall 3 and an upright wall 2 extending upwardly fromthe peripheral edge of the bottom wall 3. The bottom wall 3 and theupright wall 2 cooperatively define an integral box-shaped moldstructure. In the model I shown in FIGS. 1(a) and 1(b), the thickness ofthe bottom wall 3 and the thickness of the peripheral upright wall 2 arethe same and the surface area of the upright wall 2 is not more thanone-half of the area of the bottom wall 3.

In an experiment, an external bending and twisting force was exerted onthe model I shown in FIGS. 1(a) and 1(b), and the internal stressgenerated against the external force was monitored. As to the results, arelatively large stress was generated on the peripheral upright wall 2,but almost no stress was generated on the bottom wall 3 having therelatively larger surface area.

In the model II shown in FIG. 1(c), the thickness of the peripheralupright wall 2 was increased to disperse the stress and, on the otherhand, the thickness of the bottom wall 3 was reduced since it does notdirectly bear the stress, so that the entire volume of the housing wall,i.e., the weight of the housing, could be minimized. Thus, thedeformation caused by an external force could be minimized.

In a model of the molded product of a housing structure shown in FIG. 2,a resistance force against the deformation was simulated. In FIG. 3(a),a model as shown in FIG. 2 was used, wherein the thickness of the bottomwall 3 and the thickness of the peripheral upright wall 2 are both 1.0mm. The left side periphery of the housing was completely fixed.Conversely, a twisting force was exerted on the right side periphery ofthe housing, i.e., an upward force of 2 kg was exerted on the right rearcorner thereof and, on the other hand, a downward force of 2 kg wasexerted on the right front corner thereof. In FIG. 3(b), the thicknessof the peripheral upright wall 2 was 2.0 mm and the other conditionswere the same as FIG. 3(a).

The results were as follows. In the case of FIG. 3(a), the maximumdeformation was 5.3 mm at the right front corner and the maximuminternal stress was 7 kgf/cm² at the left side periphery. Conversely, inthe case of FIG. 3(b), the maximum deformation was 3.1 mm and themaximum internal stress was 4 kgf/cm². Thus, both the maximumdeformation and the maximum internal stress were significantly reduced.

As shown in FIG. 2(a) housing is provided with several cylindricalbosses 5 which can be used for receiving the screws, particularly,tapping screws snap fittings, or insert threads, for affixing thereto aprinted circuit board, connectors, or a housing cover.

In injection molding of a plastic housing, if the knockout pins 11 (seeFIG. 5) were arranged only on the thin wall portion the molded productwould be pushed by contact at its weakest positions and thus,deformation would be increased. Therefore, according to the presentinvention, cylindrical bosses 5 are arranged on the intermediatepositions or on the intersections of the ribs 4. Thus, these cylindricalbosses 5 are pushed by a cylindrical sleeve or knockout pin, so that theexerted force can be dispersed by the ribs 4 to the thin wall portionand, therefore, the deformation can be minimized.

FIG. 2(a) is a plan view of the molded product of a housing structureaccording to the present invention, and FIG. 2(b) is a cross-sectionalview taken along line b--b in FIG. 2(a).

This embodiment is a body cover (housing ) of a notebook type personaluse computer which is A4 sized and has a bottom wall 3 of 1.0 mmthickness, a peripheral upright wall 2 of 15 mm height and 2.0 mmthickness, and X-shaped cross ribs 4 on the bottom wall 3. This housingwas made by injection molding of a new material, i.e., denatured ormodified polyphenylene oxide containing carbon fibers. For comparingwith this embodiment, an comparative example of the housing was made inthe same manner as the above, except that the thickness of theperipheral upright wall 2 was 1.0 mm.

The left side periphery of each sample thus made was completely fixed.Conversely, a twisting force was exerted on the right side periphery ofthe housing, i.e., a downward force of 2 kg was exerted on the rightfront corner thereof and, on the other hand, a upward force of 2 kg wasexerted on the right rear corner thereof. The stress thus generated inthe housing and the deformation thereof were measured by a monitoringrobot. The results were as follows. The maximum deformation of thisembodiment was 3.0 mm, but the maximum deformation of the comparativeexample was 5.8 mm. It should be noted that the results were quitesimilar to the results of the simulation testing, as mentioned above. Inthe embodiment, the deformation could be significantly reduced byincreasing the thickness of the peripheral upright wall 2 by only 1.0mm, with an increase of the weight by only 10 g.

If the thickness of the bottom wall 3 was less than 0.6 mm, a housinghaving a large bottom wall could not be obtained. Conversely, if thethickness of the bottom wall 3 was more than 2.5 mm, it would beimpossible to obtain a light weight housing as compared with aconventional housing. Also, if the thickness of the peripheral uprightwall 2 was more than 3.0 mm, it would also be impossible to reduce theweight of the housing, although the strength thereof could be increased.

FIG. 4 shows the results of a simulation of resin flow for determining amold structure. In this embodiment, the model is a notebook typepersonal use computer which is A4 sized and has a bottom wall 3 of 1.0mm thickness and a peripheral upright wall 2 of 10 mm height. The rearportion of this peripheral upright wall 2 of 18 mm height is providedwith a mounting hole, such as for a connector. The bottom wall 3 isprovided with X-shaped cross ribs 4 of 5×5 mm. Also, four gates atearranged on the ribs and three gates (gates are indicated by trianglemarks as shown in FIG. 4) are arranged on the thin plate portions of 1.0mm thickness which are not provided with ribs 4 to facilitate flowing ofthe molten plastic in that area. Each of the gates arranged on acorresponding thin plate portion is provided with a button-likereceiving portion. The results of the simulation were, as shown in FIG.4, that the resin enters the mold cavity through the seven gates and thebottom wall is formed with six flow ends 1 to 6 where gas accumulates.

FIG. 5 is a cross-sectional view of an embodiment of a mold structureaccording to the present invention and FIGS. 6(a), 6(b), 6(c) and 6(d)show embodiments of a boss and/or knockout pin engaging structure. Themold structure associated with a molded product 9 shown in FIG. 5comprises a lower mold 6, an intermediate mold 7, and an upper mold 8.The upper mold 8 is provided with gates 10 and 10' which provide inletsfor the molten resin and is provided at the positions of the gasaccumulation with knockout pins 11 each having a sintered metal tip.Also, in order to reduce the deformation when the molded product isdischarged from the cavity, as shown in FIG. 6(a), the molded product 9further is provided, on the ribs 4 or on the intersection of the ribs 4,with cylindrical bosses 5 which are used as the main knockout pinengaging structures. In addition, as shown in FIGS. 6(c) and 6(d), themold 12 is provided with sleeve-like knockout pins 11 and fixing pins13, so that the molded products 9 can be pushed out of the cavity, asshown in FIG. 6(d). The cylindrical bosses 5 thus formed by the moldthereafter can be used as connectors e.g., as screw holes, for receivingscrews, particularly, tapping screws, snap fittings, or insert threads,for affixing a printed circuit board, connectors, or a housing coverthereto, as shown in FIG. 6(b).

According to the mold structure of the present invention, the ribportions 4 and a relatively thick peripheral upright wall 2 are used aspassageway for the molten resin in the injection molding and, therefore,the gates 10 and 10' can be arranged on the rib portions 4 or on atleast two positions in the vicinity of the peripheral upright wall 2, sothat the resin can more smoothly flow. Also at, the positions of thebottom wall, to which the resin finally reaches there are provided,telescopic or knockout pins each having a structure through which theair (i.e., gas) easily escapes (for example, a structure having a gap, agroove-like vent, sintered alloy, or the like) are provided. Thus, resinfiring due to overheating of the resin by a short shot or adiabaticcompression of the air is prevented.

Thus, according to the mold structure of the present invention, a thinmolded product can be obtained without a short shot, deformation andgas-firing. In an embodiment of the housing used for the notebook typecomputer, a weight of the housing can be reduced to about 350 g byreducing the thickness of the main wall to 1.0 mm, as compared with aconventional type housing having a weight of about 750 g. In this case,the deformation of the embodiment due to an external force issubstantially the same as a conventional housing.

FIG. 7 is a plan view of a housing structure applied to this invention,i.e., a lower cover of a personal use notebook type computer of a typein practical use. As will be seen in FIG. 7, the shape of this housingis more complicated when compared with the embodiment shown in FIGS.2(a) and 2(b), although the principle of this invention is also appliedto this housing. Namely, the thickness of the bottom wall is in therange of two-thirds to one-third with respect to the thickness of theperipheral upright wall, e.g., the thickness of the bottom wall is 1.0mm and the thickness of the peripheral upright wall is 2.0 mm. There aremany ribs in this example and, in the same manner as the above, theseribs can be used as passageways for flowing therethrough the moltenresin.

It should be understood by those skilled in the art that the foregoingdescription relates to only a preferred embodiment of the disclosedinvention, and that various changes and modifications may be made to theinvention without departing from the spirit and scope thereof.

We claim:
 1. A box-shaped plastic housing comprising:a substantiallyplanar bottom wall having a peripheral edge, an upright wall integrallyjoined at a bottom edge thereof to, and extending upwardly from, saidperipheral edge of said bottom wall, said bottom wall and said uprightwall cooperatively defining an integral, box-shaped molded structure,and said bottom wall having a thickness in the range of from two-thirdsto one-third the thickness of said upright wall; and said bottom walland said upright wall having respective inner surfaces cooperativelydefining the inside surface of said box-shaped structure, and saidbottom wall further comprises at least one rib structure formedintegrally on said inner surface thereof, each rib structure extendingalong a respective direction relative to said inner surface andassociated peripheral edge of said bottom wall.
 2. A box-shaped plastichousing as set forth in claim 1, further comprising a cylindrical bossformed on a respective rib structure and having an axis perpendicular tothe direction along which said respective rib structure extends, saidcylindrical boss defining a connector and a knock-out pin engagingstructure.
 3. A box-shaped plastic housing as set forth in claim 1,further comprising first and second said rib structures extending inrespective, first and second intersecting directions such that theycross each other and form an integral intersection therebetween, saidcylindrical boss being formed on said first and second rib structures atsaid integral intersection therebetween and having an axis perpendicularto each of the first and second directions.
 4. A box-shaped plastichousing for a portable-type electronic unit of integrally molded resin,said housing being made by injection molding and comprising:asubstantially planar and rectangular bottom wall having a peripheraledge, an upright wall integrally joined at a bottom edge thereof to, andextending upwardly from, said peripheral edge of said bottom wall, saidbottom wall and said upright wall cooperatively defining an integral,box-shaped molded structure, said bottom wall and said upright wallhaving respective surface areas, the surface area of said upright wallbeing not more than one-half of the surface area of said bottom wall andsaid bottom wall having a thickness in the range of from two-thirds toone-third the thickness of said upright wall; and said bottom wall andsaid upright wall having respective inner surfaces cooperativelydefining the inside surface of said box-shaped structure, and saidbottom wall further comprises at least one rib structure formedintegrally on said inner surface thereof, each rib structure extendingalong a respective direction relative to said inner surface andassociated peripheral edge of said bottom wall.
 5. A box-shaped plastichousing as set forth in claim 4, further comprising a cylindrical bossformed on a respective rib structure and having an axis perpendicular tothe direction along which said respective rib structure extends, saidcylindrical boss defining a connector and a knock-out pin engagingstructure.
 6. A box-shaped plastic housing as set forth in claim 4,further comprising first and second said rib structures extending inrespective, first and second intersecting directions such that theycross each other and form an integral intersection therebetween, saidcylindrical boss being formed on said first and second rib structures atsaid integral intersection therebetween and having an axis perpendicularto each of the first and second directions.
 7. A box-shaped plastichousing as set forth in claim 1, wherein said upright wall has anaverage thickness of not more than 3.0 mm.
 8. A box-shaped plastichousing as set forth in claim 1, wherein said bottom wall and saidupright wall have respective surface areas, the surface area of saidupright wall being not more than one-half of the surface area of saidbottom wall.
 9. A box-shaped plastic housing as set forth in claim 4,wherein said upright wall has an average thickness of not more than 3.0mm.